1. Field of the Invention
The present invention is generally related to ophthalmic instruments and surgery. In a particular embodiment, the invention provides a mechanism and method for scanning a laser beam over a surface of a patient""s eye to effect resculpting.
Laser-based systems are now used in ophthalmological surgery on the surface of the cornea to correct vision defects. These systems use lasers to achieve a desired change in corneal shape, with the laser removing thin layers of corneal tissue using a technique generally described as ablative photodecomposition. These laser eye surgery techniques are useful in procedures such as photorefractive keratectomy, phototherapeutic keratectomy, laser insitu keratomileusis (LASIK), and the like.
The ability to track or follow movements of a patient""s tissue is recognized as a desirable feature in laser eye surgery systems. Movements of the eye include both voluntary movements and involuntary movements. In other words, even when the patient is holding xe2x80x9csteadyxe2x80x9d fixation on a visual target, eye movement still occurs. Tracking of the eye during laser eye surgery has been proposed to avoid uncomfortable structures which attempt to achieve total immobilization of the eye. Tracking may enhance known laser eye surgery procedures, and may also facilitate new procedures, such as treatment of irregular astigmatism.
A variety of structures and techniques have been proposed for both tracking of eye movements and scanning of a laser beam across the corneal tissue. An exemplary xe2x80x9coffset imagingxe2x80x9d scanning system is described in European Patent Application Publication No. 628298, the full disclosure of which is hereby incorporated by reference. This offset imaging system allows a relatively large beam to be accurately directed onto the corneal surface so as to mitigate myopia, hyperopia, astigmatism, and combinations of these ocular defects, particularly when the scanning or offset imaging system is combined with one or more variable apertures for profiling the laser beam. As described in co-pending U.S. patent application Ser. No. 09/274,499, filed Mar. 23, 1999, and entitled Multiple Beam Laser Sculpting System and Method, the laser beam may ideally be separated into a plurality of beamlets to minimize discontinuities adjacent the ablation edges.
Although known scanning systems have proven both effective and safe for resculpting the cornea to improve vision, work in connection with the present invention has shown that integrating eye tracking capabilities into known laser eye surgery systems can present additional challenges. Specifically, laser eye surgery systems having eye tracking capabilities would benefit from enhanced response time of the beam deflection mechanism. Although alternative scanning systems having potentially faster response times have been described, the offset imaging system described above remains popular, possibly in part because of the combination of accuracy of safety provided by this known mechanism.
In light of the above, it would be desirable to provide improved laser eye surgery systems, devices, and methods. It would be particularly beneficial if these improvements provided enhanced scanning techniques which maintained the accuracy and safety of known scanning systems, and provided faster response times. It would be particularly beneficial if these improvements allowed the incorporation of eye trackers into known laser eye surgery systems, ideally without having to modify the entire optical train and control architecture.
2. The Background Art
As described above, European Patent Application Publication No. 682298 entitled xe2x80x9cSystem for Laser Treatment of Refractive Errorsxe2x80x9d describes an exemplary scanning mechanism for use in laser eye surgery. Alternative scanning mechanisms and related structures and methods are described in U.S. Pat. Nos. 4,669,466; 4,665,913; 5,782,822; 5,599,340; 5,520,679; 4,887,019; 5,391,165; 5,683,379; and 5,505,723; the fall disclosures of which are incorporated herein by reference.
The present invention generally provides laser eye surgery systems, methods, and devices. The invention makes use of a two-pivot scanning system for laterally deflecting the laser beam across the corneal surface in two dimensions (sometimes called X-Y scanning). In the exemplary embodiment, an imaging lens pivots about two eccentric pivots having pivotal axes extending along, but disposed outside the laser beam. As the lens pivots along one of the two axes, the beam will follow an arc-shaped path. The eccentric axes are typically perpendicular to the laser beam and are ideally offset from each other about the laser beam axis by about 90xc2x0, so that pivoting of the imaging lens about the second eccentric axis will move the laser along an orthogonal arc-shaped path. The system controller can compensate for these arc-shaped path deflections by adjusting the angular position of the complementary axes, thereby allowing the beam to be accurately directed at a target location throughout a target X-Y region of the corneal surface.
In a first aspect, the invention provides a laser eye surgery system for modifying a cornea of a patient. The system comprises a laser generating a laser beam for selectively ablating the cornea. The laser beam defines a beam axis. A first stage is pivotable relative to the laser about a first axis offset laterally from the beam. A second stage is pivotable relative to the first stage about a second axis offset laterally from the beam. An optical element is mounted to the second stage in an optical path of the laser beam. The optical element deflects the beam laterally with pivoting of the first and second stages.
The optical element will preferably comprise an imaging lens. A controller will often be coupled to the first and second stages so that the stages pivot in response to signals from the controller. The controller may compensate for arc-shaped beam deflection paths of the beam to accurately direct the laser beam at a target location.
Preferably, the first stage will pivot relative to a fixed support structure by driving engagement of a first motor which is fixed relative to a fixed support structure. The first stage may carry a pivotal joint coupling the first stage to a second stage, so that the second eccentric axis moves with the first stage. A second drive motor may be mounted to the first stage, with the second drive motor drivingly engaging the second stage. Sensors will preferably indicate stage angular positions to the controller to ensure targeting accuracy.
In another aspect, the invention provides a laser eye surgery system for modifying a cornea of a patient. The system comprises a laser generating a laser beam for selectively ablating the cornea. The laser beam defines a beam axis. An optical train in an optical path of the laser beam directs the laser beam toward the cornea. A first offset mechanism pivots at least a portion of the optical train about a first eccentric axis. A second offset mechanism pivots at least a portion of the optical train about a second eccentric axis. The first eccentric axis and the second eccentric axis extend along the beam axis and are offset relative to each other circumferentially about the beam, often by 90xc2x0.
In another aspect, the invention provides a scanning system for use with a laser eye surgery system. The laser system has a laser producing a laser beam for selectively resculpting a cornea according to signals from a controller. The scanning system comprises a first stage which pivots relative to the laser about a first axis in response to the control signals. The first axis is offset laterally from the beam axis. A second stage is pivotably mounted to the first stage. The second stage pivots about a second axis offset laterally from the beam axis in response to the control signals. An optical element is mounted to the second stage in an optical path of the laser beam to deflect the beam laterally according to the control signals so as to effect the desired resculpting.
In a method aspect, the invention allows redirecting of a corneal resculpting laser beam. The method comprises deflecting a beam along a substantially arc-shaped path by rotating an optical element about a first pivot or axis offset laterally from the beam. The beam is deflected along a substantially arc-shaped path by rotating the optical element about a second pivot or axis offset laterally from the beam, and offset circumferentially about the beam from the first axis. Typically, the pivots are offset by about 90xc2x0 relative to the beam. The two intercepting arc-shaped beam deflection paths which this method can provide allow substantially rectangular coverage of a patient""s cornea.